Circumstellar Dust Formation around the Mira-Variable NML Tauri \\Determined by 11 Micron Spatial Interferometry
Session 35 -- ISM: Abundances and Dust
Display presentation, Wednesday, June 14, 1995, 9:20am - 6:30pm

## [35.14] Circumstellar Dust Formation around the Mira-Variable NML Tauri \\Determined by 11 Micron Spatial Interferometry

David D.S. Hale (Univ. of Pittsburgh), M. Bester, W.C. Danchi, C.G. Degiacomi, \& C.H. Townes (Univ. of California, Berkeley)

Visibility of the Mira-variable NML Tauri (also known as IK Tau) is measured with the U.C. Berkeley Infrared Spatial Interferometer (ISI). The ISI is comprised of two movable 1.65 m telescopes and is currently using heterodyne detection at a wavelength of 11.15 $\mu$m. New visibility data being reported here are obtained using the ISI 4 m (E-W) and 9 m (33$\deg$ N of E) baselines, during the star's visual luminosity phase near $\phi=0.45$ and $\phi=0.62$, respectively. These data are compared with earlier measurements which were made using the ISI 13 m ($23\deg$ N of E) baseline, at a visual luminosity phase of $\phi=0.82$. The dust shell is modeled reasonably well by a spherical distribution having an inner radius of about 5 stellar radii and density inversely proportional to the square of the radius, as expected from constant emission of material. However, there are significant deviations from this theoretical visibility curve, and these deviations have changed over time. The change suggests that a particular dust structure is moving away from the star at a velocity of 22 km/s, the expansion rate measured by Doppler effects in the gaseous component of the shell.